SSHFS: Super Easy File Access over SSH

As you can see from the above examples, I needed to type my password to complete the SSH connection to the remote system. This can be eliminated by creating a trust relationship between the local and remote user accounts. This is not appropriate in all situations, because it essentially makes the accounts equivalent from a security perspective. Any malicious activity on one account can spread to other systems via the trust, so take caution and fully understand the implications of setting up trust relationships. To begin setting this up, you need to create an SSH key pair, which consists of public and private key files named id_rsa and id_rsa.pub, respectively.

The public key is copied to the remote system and placed in the $HOME/.ssh/authorized_keys file. Some systems may use the filename authorized_keys2 in addition to or instead of authorized_keys.

This allows any user in possession of the private key to authenticate without a password. We create the key pair using the command ssh-keygen. The files are placed in the proper locations automatically on the local system in the $HOME/.ssh directory. Because we already have my remote home directory mounted, appending the public key to the authorized_keys file is extra easy. Below are all the steps required (assuming you created the equivalent of the randombox_home directory and mounted it):

$ cd $HOME
$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/matt/.ssh/id_rsa): <ENTER>
Enter passphrase (empty for no passphrase):  <ENTER>
Enter same passphrase again:  <ENTER>
Your identification has been saved in /home/matt/.ssh/id_rsa.
Your public key has been saved in /home/matt/.ssh/id_rsa.pub.
The key fingerprint is:
fa:e7:7c:e1:cb:7b:66:8b:67:07:05:99:7f:05:b9:4a matt@myworkstation
$ mkdir randombox_home/.ssh
$ chmod 700 randombox_home/.ssh
$ cat .ssh/id_rsa.pub >> randombox_home/.ssh/authorized_keys
$ chmod 600 randombox_home/.ssh/authorized_keys

In the above example, we create the key pair with an empty passphrase, then append the public key to the authorized_keys file in the remote home directory and set the permissions. After this is done, I no longer need to type the password when connecting to the remote account. To test this, first we unmount the remote home directory with the following command:

$ fusermount -u randombox_home

To test the trust relationship, we can try to run the uptime command on the remote system:

$ ssh matt@my.randombox.com uptime
12:20:40  up 38 days,  4:12,  0 users,  load average: 0.11, 0.04, 0.01

Good, no password needed. The trust relationship is working properly. If you have trouble getting this trust relationship to work, check the permissions on the files in .ssh on both systems. Many times lax permissions prevent SSH from using key files. Also, take a look at the syslog log files. OpenSSH's sshd server logs messages into syslog, which often are helpful in diagnosing key file problems. You may have to increase the logging verbosity level in the sshd_config file, usually found in /etc/ssh/.

You also can debug the connection by running ssh in the above example with the -vvv option to turn up verbosity. Now, let's mount the remote directory again. This time it does not prompt for my password:

$ cd $HOME
$ mkdir randombox_home
$ sshfs  matt@my.randombox.com:  randombox_home
$ ls -l randombox_home/
-rw-r-----  1 matt users     7286 Feb 11 10:33 sshfs.article.main.txt
drwx------  1 matt users     2048 Mar 21  2001 projects
drwx------  1 matt users     2048 Dec  1  2000 Mail
drwxr-xr-x  1 matt users     4096 Jun  8  2002 public_html

In the last example, we configured and automated non-interactive mounting of a remote directory. Because we're no longer being prompted for a password, we can integrate SSHFS mounting into scripts, or better yet the GNOME desktop. To configure GNOME to mount our remote home directory automatically, we configure the SSHFS mount command as a session startup program. This is done from inside the Sessions preferences dialog. Navigate to Desktop→Preferences→More Preferences→Sessions->Add, and fill in the dialog as shown in Figure 1.

Figure 1. Set up a GNOME startup command to mount an SSHFS share.

Upon the next login, GNOME automatically mounts the remote directory for me, as you can see in Figure 2.

Figure 2. GNOME automatically mounts the remote directory.

Note that GNOME does not reliably kill this command upon exiting the session. You can unmount the remote directory manually using the fusermount -u randombox_home command. Another option is to automate the unmount by modifying the $HOME/.Xclients-default file to run the fusermount command as follows:

#!/bin/bash
# (c) 2001 Red Hat, Inc.

WM="gnome-session"
WMPATH="/usr/bin /usr/X11R6/bin /usr/local/bin"

# Kludged to run fusermount upon gnome logout.  20060301-MEH
for p in $WMPATH ; do
     [ -x $p/$WM ] && $p/$WM; fusermount  -u randombox_home; exit 0
done

exit 1

Be aware that the .Xclients-default file is rewritten every time you run the switchdesk utility. You have to modify this file every time you use use the switchdesk utility to change your default desktop windowing manager.

Finally, you can add the appropriate sshfs commands in the boot startup file that is appropriate for your distribution. This way, your system will mount all the SSHFS directories automatically each time you boot your desktop.